The invention relates to fuel cell power plants and, more particularly, to a cell stack assembly with integrated auxiliary water recovery device for expanding the operating parameters of the cell stack assembly.
Fuel cell power plants are well known and are commonly used to produce electrical energy from reducing and oxidizing fluids to power various electrical apparatus. In such power plants, a plurality of planar fuel cells are typically arranged in a stack surrounded by an electrically insulating frame that defines manifolds for directing flow of reducing fluid, oxidizing fluid, coolant and product streams. Each individual cell generally includes an anode electrode and a cathode electrode separated by an electrolyte. A reactant or reducing fluid such as hydrogen is supplied to the anode electrode, and an oxidant such as oxygen or air is supplied to the cathode electrode. In a cell utilizing a proton exchange membrane (PEM) as the electrolyte, the hydrogen electrochemically reacts at the anode catalyst to produce hydrogen ions and electrodes. The electrodes are conducted to an external load circuit and then returned to the cathode electrode, while the hydrogen ions transfer through the electrolyte to the cathode electrode, where they react with the oxidant and electrodes to produce water and release thermal energy.
In operation of a fuel cell employing a PEM, the membrane is saturated with water, and the anode electrode adjacent to the membrane must remain at least partially saturated with H2O. Product water formed at the cathode electrode that is not removed through a water transport plate as shown in commonly owned U.S. Pat. No. 5,853,909 is removed by evaporation or entrainment into a circulating gaseous stream of oxidant, and can be lost if not recovered from the stream prior to venting. It is critical, however, that proper water balance be maintained between a rate at which water is produced at the cathode electrode, and rates at which water is removed from the cell. Thus, it is critical to recover sufficient water from the exhaust stream such that water lost in the exhaust stream is made up from water obtained from incoming reactants and that produced in the cell.
Numerous methods and efforts have been undertaken to recover such water. Typically, these efforts lead to additional equipment and the like that typically add weight and volume. However, one primary area of interest for use of fuel cell power plants is in automotive applications, where space and weight are critical.
Thus, the need remains for space and weight-efficient methods and structures for maintaining water balance in fuel cell power plants so as to expand the operating parameters of use for same.
It is the primary object of the present invention to provide such a structure and method.
Other objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages have been readily attained.
According to the invention, a cell stack assembly is provided which comprises a plurality of plates defining a primary cell stack portion having a primary air flow path, a fuel flow path and a primary coolant flow path; and an auxiliary coolant stack portion defining an auxiliary air flow path and an auxiliary coolant flow path, said auxiliary air flow path being communicated with said primary air flow path, wherein water is condensed from air in said auxiliary air flow path.
In further accordance with the present invention, a method for enhancing water recovery from a cell stack assembly is provided, which method comprises the steps of providing a cell stack assembly comprising a plurality of plates defining a primary cell stack portion having a primary air flow path, a fuel flow path and a primary coolant flow path; and an auxiliary coolant stack portion defining an auxiliary air flow path and an auxiliary coolant flow path, said auxiliary air flow path being communicated with said primary air flow path; flowing fuel through said fuel flow path and oxidant through said primary air flow path so as to generate electricity from said cell stack assembly and an at least partially saturated exhaust gas from said primary air flow path; and flowing said at least partially saturated exhaust gas through said auxiliary air flow path and an auxiliary coolant through said auxiliary coolant flow path so as to cool said at least partially saturated exhaust stream and condense water from said at least partially saturated exhaust stream.
In accordance with the present invention, auxiliary cooling of the at least partially saturated exhaust stream from at least the cathode is provided in a manner which expands the size or space occupied by the fuel cell power plant in less than or equal to one dimension of the three-dimensional space occupied by the fuel cell power plant. Further, the structure and method of the present invention substantially reduces and/or eliminates the need for external or additional flow structures to convey the exhaust stream to separate devices, and instead integrates the auxiliary water recovery into the manifold and/or plate structure of the fuel cell power plant.